Regioregular poly(3-hexylthiophene) (P3HT) or poly(quaterthiophene) (PQT) have been used as semiconductors in organic thin film transistors (OTFT) or organic photovoltaic (OPV) cells. Regioregular P3HT or PQT exhibit a charge mobility of 0.1 to 0.2 cm2/Vs when applied by spin-coating, but significantly lower when applied by a solution-based printing process. Further, P3HT has a wide bandgap of about 1.9 eV. A wider bandgap limits the absorbance of light with higher wavelengths, and consequently the power conversion efficiency (PCE) for sunlight. For example, calculation shows that with a bandgap of 1.9 eV, only about 22% of light with a 650 nm wavelength can be absorbed. It has been reported that the PCE for a P3HT based device is only up to 5% (see Ma, W. L. et al., “Thermally stable, efficient polymer solar cells with nanoscale control of the interpenetrating network morphology,” Adv. Funct. Mater., 2005, vol. 15, p. 1617. Narrowing polymeric bandgap can increase the amount of absorbed sunlight, but does not necessarily improve power conversion efficiency, as it can also decrease the equivalent open circuit voltage of the OPV cell. This can lead to a decrease in power conversion efficiency, which offsets the gain from narrowed bandgap. A reported PCE for a device based on known low bandgap polymer OPV materials is only up to 7.73% (see Hsiang-Yu Chen et. al., “Polymer solar cells with enhanced open-circuit voltage and efficiency,” Nature Photonics, 2009, vol. 3, pp. 649-653.